I havent had my yfz450 long. 2004 but great shape. I dont know but a few of the mods. No air lid, foam filter, HMF full racing exhaust and jet kit. I dont know what the jets are in it but I do have the new ones to rejet if needed. I have a bad pop on deceleration and My header is glowing all the way back. The red anodized is starting to discolor as well. Looks to me as running rich. Havent pulled the plug yet to see. I did replace the header gasket to make sure no leaks. Altitude I have no clue about here. I did make a short video to see it seems to run fine. any ideas and I will give it a try tomorrow. I know where the main jet is but not the other as far as location to get to it. If links to youtube arent allowed please let me know.